1. Field of the Invention
The invention relates to low dielectric constant materials, in particular materials comprising siloxanes.
2. Discussion of the Related Art
As integrated circuit device integration densities rise and circuit dimensions shrink, certain problems are encountered. For example, the smaller line dimensions increase the resistivity of the metal lines, and the narrower interline spacing increases the capacitance between the lines. This increased resistance and capacitance causes problems in propagation delay, crosstalk noise, and power dissipation. Moreover, as the device speed increases due to smaller feature sizes, the resistance-capacitance (RC) delay caused by the increased resistivity and capacitance will tend to be the major fraction of the total delay (transistor delay+interconnect delay) limiting the overall chip performance. It is therefore desirable to reduce the increased resistance and capacitance in integrated circuit applications.
To address these problems, new materials for use as metal lines and interlayer dielectrics (ILD), as well as alternative architectures, have been proposed to replace the current SiO.sub.2 -based interconnect technology. These alternative architectures will require the introduction of low dielectric constant (.kappa.&lt;3) materials as the interlayer dielectric and/or low resistivity conductors such as copper.
It is desired that new low .kappa. materials exhibit a variety of electrical, chemical, mechanical and thermal properties. These properties include low dielectric constant, high thermal stability, good adhesion, low stress, good mechanical properties, etchability and etch selectivity, low moisture absorption, high thermal conductivity, low leakage current, high breakdown strength, and easy and inexpensive manufacturability.
A variety of low .kappa. materials have been proposed to meet some or all of these criteria. The materials are typically produced by chemical vapor deposition (CVD) or by spin-on coating. Materials produced by CVD include fluorinated SiO.sub.2 glass (.kappa.=3.5), fluorinated amorphous carbon, and polymers such as the parylene and polynaphthalene families, and polytetrafluoroethylene (PTFE) (K=2.7-3.5 for nonfluorinated polymers and 1.8-3.0 for fluorinated polymers). Materials deposited by spin-on coating include organic polymers, morganic polymers, inorganic-organic hybrids, and porous materials such as xerogels or aerogels. Organic materials typically offer lower dielectric constants than inorganic materials but, in some cases, can exhibit undesirably low thermal stability and poor mechanical properties.
One approach to polymeric low .kappa. materials has been the use of porous organic polymers. See, e.g., U.S. Pat. Nos. 5,895,263, 5,773,197, and 5,883,219, the disclosures of which are hereby incorporated by reference. See also J. Remenar et al., "Dendri-Glass-Design of Ultra-low Dielectric Constant Materials Using Specialty Highly Branched Polymers," Polymer Preprints, Vol. 39, No. 1 (March 1998); and R. Miller et al., "Porous Organosilicates as Low-.kappa. Insulators for Dielectric Applications," Abstract No. 01.2, MRS Spring 99 Meeting. These articles relate to methyl- or methy/phenyl-silsesquioxane resins with organic macromolecular pore generators, referred to as porogens. These porogens are capable of being decomposed after the resin is cured to leave nanoscopic pores. But a careful heating regime is generally required to prevent pore collapse as well as cracking. Also, methylsilsesquioxane-based materials tend to be brittle, and thus prone to cracking due to thermal-mechanical shock. (This problem was orally presented by R. Miller at the MRS Spring 1999 Meeting.) The cracking problem is particularly acute when the materials are deposited in several layers, which is typically the case.
Thus, organic low .kappa. materials are desired, where the materials exhibit a variety of desirable properties, particularly good crack resistance at the elevated temperatures experienced during fabrication of an IC device.